Sure. This one https://s.codepen.io/joshhunt/debug/ZKyYNz. It differs to IE, Safari and Chrome in the way it treats height:0 padding-top: 100% on a flex child. In Safari, the grey box expands properly to contain all divs. In Firefox, it doesn't.

Granted, this is more of a flexbox spec issue (last time I checked this behaviour is intentionally undefined), but it's still an annoying case of one browser doing something all the others don't.